1. Field of the Invention
This invention relates generally to the field of systems for processing of large substrates, and more particularly to high-throughput electron-beam flat panel display substrate (FPDS) testing systems.
2. Description of the Related Art
The use of electron beams to inspect and electrically test flat panel display (FPD) substrates (FPDSs) is an established technique. For FPDS testing, it is necessary to be able to test 100% of the pixels on the FPDS surface since, typically, a display with more than a few defective pixels is unusable. In some cases, if defective pixels are detected early enough in the manufacturing process, these pixels can be repaired. In other cases, if a substrate is found to have numerous defective pixels, it is more economical to scrap that FPDS prior to further processing. FPDS testing also provides process feedback: if successive FPDSs show increasing numbers of defective pixels, a deviation from proper process parameters (etch, deposition, lithography, etc.) may have occurred, which must be corrected quickly to restore normal production yields. 100% pixel inspection requires that every pixel on the FPDS must be able to be targeted by at least one of the electron beams from the linear column array.
Prior art e-beam systems for testing FPDSs employ a process chamber, pumped down to high vacuum, for containing one or more electron beam columns. The electron beams generated by these columns are scanned across the surface of the FPDS under test, thereby causing the emission of secondary electrons (SEs) and backscattered electrons (BSEs) which are collected by a detector, as is familiar to those skilled in the art. A typical FPD has a large number of pixels, arranged in an X-Y array, each consisting of a thin-film transistor connected to a large pixel electrode. For proper operation of the FPD, it is necessary for nearly all pixels to be functional. During FPD fabrication, large numbers of pixels are connected together to “shorting bars”, which, in turn, are connected to test pads around the periphery of each FPD on the FPDS. For electrical testing of the FPDS, connections are made to each of these test pads and voltages are thereby applied to the pixels in all of the FPDs on the FPDS. These electrical connections are typically made using a “probe frame”, which contains a large number of contactors physically arranged to match the placement of test pads on the FPDS. After insertion of an FPDS into the process chamber, the probe frame (or its functional equivalent) is lowered onto the FPDS. Then, using the electron beams from the columns in the process chamber, electrical measurements of pixel performance may be made in order to detect if any pixels are defective.
Prior art testing systems typically employ a loadlock, attached to the process chamber, into which FPDSs for testing are loaded, pumped down, then inserted into the process chamber. After the probe frame has been lowered onto the FPDS, it may be aligned with the FPDS. If alignment is performed, no e-beam testing can be performed during the alignment process, representing a loss in system throughput. FPDSs are typically >2 m in X-Y, but <1 mm thick, and are made of glass—transporting such a delicate object clearly represents a significant difficulty, both in terms of throughput (i.e., the maximum transport speed and acceleration may be limited), and in terms of potential breakage within the system (leading to system downtime). After e-beam testing of the FPDS is completed, the probe frame is lifted off the FPDS, and the FPDS is then removed from the process chamber, followed by insertion of another FPDS into the process chamber, etc.
FIG. 1 is a schematic of a prior art multiple electron beam FPDS testing system. A typical FPDS contains a number of flat panel displays (FPDs)—six FPDs are shown in the FPDS 1398 of FIG. 1. Each FPD contains a large number of pixels arranged in an X-Y configuration. At the stage of FPD manufacturing where e-beam testing is normally performed, each pixel typically comprises a thin-film transistor (TFT) connected to a pixel electrode (generally larger than 100 μm in both dimensions). To facilitate testing, a large number of the TFT sources are shorted together with shorting bars, connected to test pads (TPs) around the periphery of each FPD on the FPDS. Similarly, large numbers of the TFT gates are also shorted together to other shorting bars, connected to another set of TPs. The prior art e-beam testing process is discussed in U.S. patent application Ser. No. 11/225,376 filed Sep. 12, 2005 incorporated by reference herein. In prior art abeam FPDS testing systems as shown in FIG. 1, after the FPDS 1398 to be tested has been inserted into the process chamber (not shown), probe frame 1399 is lowered onto FPDS 1398. Probe frame 1399 contains a large number of contactors (not shown) which must align with, and make good electrical contact to, every one of the TPs on the FPDS. If any contactors fail to make contact with the TPs, it will not be possible to fully test the FPDS, with the result that substantial numbers of defective pixels may go undetected. Since the TPs are generally positioned around the border of each FPD, and the FPDS contains a number of FPDs, probe frame 1399 must be designed with connections both to the perimeter and the middle of the FPDS—the cross-members in probe frame 1399 crossing FPDS 1398 contain these connections.
In FIG. 1, four electron beam columns 1311 generate electron beams 1330, each being scanned over an area of the FPDS 1398 typically >300 mm square. The impact of the electron beams 1330 with FPDS 1398 causes the emission of secondary electrons (SEs) and backscattered electrons (BSEs). Signal electrons 1395 may comprise only SEs, only BSEs, or a mixture of SEs and BSEs. The electron optics is configured to ensure than the signal electrons 1395 from each beam 1330 are collected only by the detector 1390 associated with that particular beam 1330 in order to avoid cross-talk between pixel test signals.
Because the square scan areas of the beams 1330 do not fully span the width of FPDS 1398, it is necessary to mount FPDS 1398 on an X-Y stage in order to position any point on the FPDS 1398 surface under one of the beams 1330. The stage comprises motion axis position sensors 1386 and 1387 and stage motors 1360 and 1361, as is familiar to those skilled in the art. Because the dimensions of the FPDS are >2 m in each axis, the X-Y stage must be very large, leading to high cost and potential reliability and maintenance issues. It would be advantageous to eliminate the need for an X-Y stage in an FPDS testing system.
Cables 1312 connect columns 1311 to optics control 1301. Cables 1391 connect detectors 1390 to detectors control 1304. Data lines 1310 connect position sensors 1386 and 1387 to X-Y position readout 1302. Cables 1325 connect stage motors 1360 and 1361 to stage control 1300. Controls 1300-1302, and 1304, are connected to system control 1303 by control links 1326, 1320, 1319, and 1392, respectively. Cable 1385 conducts control signals to the probe frame 1399 from system control 1303.
There are a number of disadvantages for prior art FPDS electron-beam testing methods:                1) The FPDS, with typical dimensions >2 m in X and Y, must be supported during testing by a large and expensive X-Y stage, which enables the FPDS to be moved around under one or more electron beams for testing of the entire FPDS surface (100% of all pixels).        2) Connection to the test pads on the FPDS requires a probe frame, which remains in the process chamber and must be aligned to the test pads for proper electrical connections. The use of a probe frame has several significant disadvantages:                    a. The probe frame-to-FPDS alignment step is performed within the process chamber—it is not possible to test the FPDS during this step, thus system throughput is adversely affected. In addition, it may be more difficult to achieve good alignment due to the difficulty of working within the confines of the process chamber.            b. If the probe frame-to-FPDS alignment is accelerated or omitted to improve throughput, there will be cases in which some test pads are not connected to the testing system electronics, causing large numbers of pixels to go untested.            c. When there is a change in the FPDS design, the process chamber must be opened to replace the probe frame since the probe frame design must be consistent with the particular arrangement of test pads on the FPDS. This has a serious negative impact on throughput and tool availability.            d. If there is a failure of the probe frame, the process chamber must be opened for replacement or repair of the probe frame—during this time, the system is down.            e. Because prior art systems use an X-Y stage to move the FPDS during testing, moving cables are required to make contact to the probe frame which is moving along with the FPDS. It is well known by those skilled in the art that two major sources of system unreliability are cables and cable connectors, especially if the cables connect to a moving assembly such as the probe frame.                        3) Prior art electron-beam FPDS testing systems generally transport the FPDS without any protective surroundings, e.g. a pallet, for physical support—this raises issues of potential FPDS breakage within the FPDS testing system, leading to system downtime while fragments of the broken FPDS are removed from valves, mechanisms, pump openings, etc.        4) In prior art testing systems, when the FPD fab switches from one size FPDS to another (usually larger) size FPDS, typically either substantial changes to the testing system are required, or an entirely new testing system is needed.        
Thus there is a need for an electron-beam FPDS testing system with the following improvements from prior art e-beam FPDS testing systems:                1) Elimination of the need for a large and expensive X-Y stage for supporting the FPDS under test.        2) Elimination of a probe frame which remains in the process chamber, and substituting a method of connecting to the test pads on the FPDS which eliminates the disadvantages of prior art system designs described above.        3) Elimination of all moving cables and cable connectors between the FPDS under test and the system.        4) Adding a capability for rapid changeover from one size FPDS to another size FPDS with minimal or no system downtime.        